DESCRIPTION: (Adapted from abstract) The transcriptional transactivator Class II transactivator (CIITA) acts a "master regulator" to activate expression of a variety of genes that encode proteins that participate in the MHC class II antigen processing and presentation pathway. Inactivation of the CIITA gene abolishes constitutive and inducible expression of MHC class II and these other factors, and this is the molecular basis for certain types of the Bare Lymphocyte Syndrome. This proposal concentrates on the regulation of expression of the CIITA gene in the B lineage. CIITA is expressed in mature B cell lines, but is not expressed in myelomas, and this appears to account for the lack of expression of MHC II in the latter. Little is known about how CIITA gene expression is regulated in B cells and myelomas, and this is the focus of this proposal. In Aim 1 the investigator proposes to continue studies whose goal is to dissect the various positive and negative regulatory elements upstream of the CIITA gene, in a region shown to contain the promoter used predominantly in B cells. This Aim will involve promoter deletions and site-specific mutations, the locations of which will be guided by information regarding transcription factor binding interactions revealed by in vivo footprinting studies. In the second Aim the mechanism of CIITA repression will be studied. The master regulator PRDI-BF1 (Blimp-1) is involved in driving terminal differentiation of B cells to plasma cell phenotype, and also appears to be directly involved in the repression of CIITA gene expression. The Dr. Wright will investigate the role of this transcription factor in this process using a variety of approaches, including overexpression of PRDI-BF1, expression of dominant negative forms of this factor, changing the location of its binding site in the CIITA promoter, and inhibition of its expression using anti-sense approaches. In the final Aim, the investigator proposes to characterize the factors required for induction of CIITA transcription in B cells using such approaches such as gel shift assays. He also proposes to clone and characterize one of these factors using the yeast one-hybrid system or oligonucleotide screening of phage expression libraries.